If you press select in twilight it will switch to a classic nds style menu. There is a download play option there. If that doesn't work you could download the download play nds file (its somewhere on the internet archive)
I have an old 2ds with a broken front camera. I can't use the 3ds camera app because it defaults to the front one. Any program that tries to use the front camera crashes. I have been using 3dshell and the animal crossing amiibo camera for now. Is there any way to force it to use the outer one?